Install Windows on 2nd HD without using Bootcamp? (Bootloader / Firmware concerns)

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Bootcamp, while it is installed by default on my machine (the one in my profile info, running macOS 10.12 Sierra), will not work correctly; every workaround lead to another brick wall, and eventually Windows itself still just refused to install on the Bootcamp partition (due to the GPT/MBR hybrid volume issue).

However, as my machine has the advantage of two HDDs (macOS is on disk1, while disk0 is currently an unused storage drive), I was wondering if I could safely wipe the other drive - after formatting it to MS-DOS (FAT) or ExFAT - and use the Windows 10 installer to format it as a bootable NTFS/GPT drive (assuming even that would work, it should as the computer itself meets the minimum specs) & then just boot into Windows (installing the Bootcamp drivers manually) by holding the Option key at bootup; or would that then supersede the macOS bootloader so that Windows became the default or even only bootable OS, and if that did happen would it be possible to restore macOS as the bootable OS by using Disk Utility on my reinstall USB stick to wipe the Windows disk (&, if necessary, reinstall macOS)?

Apologies for the mass of "What if?" questions, but there are a lot of possibilities for what could go wrong & I've found very little information on people attempting such things, assuming anyone ever has...

 

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Never mind, turns-out the newer uEFI software in Windows 10 isn't properly compatible with the older uEFI firmware on that machine & so Windows 10 can only boot on it if it's the sole OS installed; and I've already got two PCs, I want my Mac to remain a Mac!